Simply because if there are an infinite number of Earth's and an infinite number of Apertures, then there are an infinite number of Apertures all doing the Perpetual Testing Initiative at the same time... Designing and stealing test chambers from each other..

So in effect Aperture on this Earth will still go bankrupt as the status quo still exists...

What Earth 1 (the main universe, that our aperture labs is in) is doing is they're slipping the blueprints to a test chamber into a different Aperture's Construction Que, or however that aperture gets it's test chambers built.

Then, Earth 1 Aperture steals that chamber back, or they send someone to test it IN that dimension, point is though, the main Aperture on Earth 1 is NOT making tests at all, they're just making the blueprints, they have completely stopped all paying and constructing of test chambers.

Therefore, no one else in the multiverse can "trick" Earth 1 Aperture because they simply aren't building anymore, and since there's an infinite amount of dumb Aperture's that are willing to pay and construct tests, this project would be a success.

See, this is what I love about stories that involve alternate realities. Any discrepancies caused by the fact that there are multiple universes, can also be resolved with the fact that there are multiple universes.